So what exactly is Focusing to Infinity? I've heard of it mentioned a few times in landscape, long distance, and astronomy photography. I was going to ask during the Google+ hangout but missed it A few comments sounded like it was good.

Infinity is simply a long way away. For a lens it's the point at which everything from a certain distance onwards is effectively in the same plane of focus. For a wide angle elns, that may be everything from a few meters away, but for a big telephoto, it may be everything beyond several hundred meters.

So say I'm doing an evening shot that is too dark for the camera to capture focus and even for me to focus manually, If I know it is far off just go to manual and focus all the way out to Infinity? Or say I'm doing some action shots that are far off (race or aircraft) I could put it on infinity so I don't have to wait for the auto-focus and slow the shot? As long as I know both shots above are far enough out for that lens?

Never set a lens to MF and go right to infinity, where the lens indicates infinity is actually SLIGHTLY past infinity, and you'll notice it. Your results will come out much less sharp than if you fine tune the shot. The best way to do this is to switch into live view, magnify part of the subject and rotate the focus ring ever so slightly until you get the perfect focus.

a useful tip, not mine I am sure I read it on the forum, is to focus your lens on a far away object during daylight hours and then put a mark on that spot. That way at night in the dark you can just put it back to that spot in manual focus.

Never set a lens to MF and go right to infinity, where the lens indicates infinity is actually SLIGHTLY past infinity, and you'll notice it. Your results will come out much less sharp than if you fine tune the shot. The best way to do this is to switch into live view, magnify part of the subject and rotate the focus ring ever so slightly until you get the perfect focus.

Indeed I noticed that before - that's why I'm using my laser pointer. The other alternative is going to infinity and back again a little bit. That works well if you get a feeling for "how much" you have to go back.

We had Termination Dust in the mountains today so I was playing an you all are correct. If I go to Infinity (Thanks Gordon now I smile everytimt I type it) It is out of focus, but if I back of just a bit it works.